Intercommunication between machines and communication between machines and humans, Machine type communication (MTC), are growing in importance. The networks of devices exchanging information are constantly growing in importance and builds up the Internet of Things (IoT). Cellular technologies adopted for these particular MTC applications are being developed and have an important role within IoT. The requirements on keeping cost and power consumption low are tough at the same time as coverage needs to be extended. All these aspects need to be addressed when designing for the future access technologies of IoT. 3GPP (3rd Generation Partnership Project) is currently investigating how to meet these design objectives and several proposals are up for discussion. The current studies have recently been moved from GERAN to RAN and have the commonality that they all have much lower system bandwidth compared to LTE (Long-Term Evolution) of today. All these so called “Clean slate” solutions target system bandwidth of around 200 kHz to enable deployment in former GSM spectrum and on existing GSM sites.
One proposal is called NB IoT (Narrowband IoT). It should be noted that NB IoT was initially referred to as NB LTE in early standardization, but was later renamed to NB IoT. Other solutions are referred to as Narrowband (NB) M2M, and NB OFDMA. Also a merged solution called NB CIoT (cellular IoT) with NB M2M uplink and NB OFDMA downlink has been proposed.
One feature of NB IoT is in-band operation, i.e., NB IoT can be deployed by puncturing LTE subcarriers one physical resource block (PRB) wide and use it for NB IoT transmission. To enable this in-band operation, it is important to synthesize the NB IoT numerologies with legacy LTE to avoid mutual interference between NB IoT and legacy LTE. In particular, NB IoT is supposed to keep LTE time-domain structure including orthogonal frequency-division multiplexing (OFDM) symbol duration and cyclic prefix (CP) duration. A straight forward solution is to reuse the sample rate to system bandwidth relation of LTE, i.e. 1.92 MHz, 3.84 MHz, 7.68 MHz, 15.36 MHz, 23.04 MHz, and 30.72 MHz sample rate related to 1.4 MHz, 3, 5 MHz, 10 MHz, 15 MHz, 20 MHz LTE channel bandwidths.